ROLL S. Anamalamudi Internet-Draft Huaiyin Institute of Technology Intended status: Standards Track M. Zhang Expires: September 6, 2018 Huawei Technologies AR. Sangi Huaiyin Institute of Technology C. Perkins Futurewei S.V.R.Anand Indian Institute of Science B. Liu Huawei Technologies March 5, 2018 Asymmetric AODV-P2P-RPL in Low-Power and Lossy Networks (LLNs) draft-ietf-roll-aodv-rpl-03 Abstract Route discovery for symmetric and asymmetric Point-to-Point (P2P) traffic flows is a desirable feature in Low power and Lossy Networks (LLNs). For that purpose, this document specifies a reactive P2P route discovery mechanism for both hop-by-hop routing and source routing: Ad Hoc On-demand Distance Vector Routing (AODV) based RPL protocol. Paired Instances are used to construct directional paths, in case some of the links between source and target node are asymmetric. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on September 6, 2018. Anamalamudi, et al. Expires September 6, 2018 [Page 1] Internet-Draft AODV-RPL March 2018 Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview of AODV-RPL . . . . . . . . . . . . . . . . . . . . 6 4. AODV-RPL DIO Options . . . . . . . . . . . . . . . . . . . . 6 4.1. AODV-RPL DIO RREQ Option . . . . . . . . . . . . . . . . 6 4.2. AODV-RPL DIO RREP Option . . . . . . . . . . . . . . . . 8 4.3. AODV-RPL DIO Target Option . . . . . . . . . . . . . . . 10 5. Symmetric and Asymmetric Routes . . . . . . . . . . . . . . . 11 6. AODV-RPL Operation . . . . . . . . . . . . . . . . . . . . . 13 6.1. Generating Route Request at OrigNode . . . . . . . . . . 13 6.2. Receiving and Forwarding Route Request . . . . . . . . . 14 6.3. Generating Route Reply at TargNode . . . . . . . . . . . 15 6.3.1. RREP-DIO for Symmetric route . . . . . . . . . . . . 15 6.3.2. RREP-DIO for Asymmetric Route . . . . . . . . . . . . 16 6.3.3. RPLInstanceID Pairing . . . . . . . . . . . . . . . . 16 6.4. Receiving and Forwarding Route Reply . . . . . . . . . . 17 7. Gratuitous RREP . . . . . . . . . . . . . . . . . . . . . . . 18 8. Operation of Trickle Timer . . . . . . . . . . . . . . . . . 19 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 9.1. New Mode of Operation: AODV-RPL . . . . . . . . . . . . . 19 9.2. AODV-RPL Options: RREQ, RREP, and Target . . . . . . . . 19 10. Security Considerations . . . . . . . . . . . . . . . . . . . 20 11. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 20 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 12.1. Normative References . . . . . . . . . . . . . . . . . . 20 12.2. Informative References . . . . . . . . . . . . . . . . . 21 Appendix A. ETX/RSSI Values to select S bit . . . . . . . . . . 21 Appendix B. Changes to version 02 . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 Anamalamudi, et al. Expires September 6, 2018 [Page 2] Internet-Draft AODV-RPL March 2018 1. Introduction RPL[RFC6550] is a IPv6 distance vector routing protocol for Low-power and Lossy Networks (LLNs), and is designed to support multiple traffic flows through a root-based Destination-Oriented Directed Acyclic Graph (DODAG). Typically, a router does not have routing information for most other routers. Consequently, for traffic between routers within the DODAG (i.e., Point-to-Point (P2P) traffic) data packets either have to traverse the root in non-storing mode, or traverse a common ancestor in storing mode. Such P2P traffic is thereby likely to traverse sub-optimal routes and may suffer severe congestion near the DAG root [RFC6997], [RFC6998]. To discover optimal paths for P2P traffic flows in RPL, P2P-RPL [RFC6997] specifies a temporary DODAG where the source acts as a temporary root. The source initiates DIOs encapsulating the P2P Route Discovery option (P2P-RDO) with an address vector for both hop- by-hop mode (H=1) and source routing mode (H=0). Subsequently, each intermediate router adds its IP address and multicasts the P2P mode DIOs, until the message reaches the target node (TargNode). TargNode sends the "Discovery Reply" object. P2P-RPL is efficient for source routing, but much less efficient for hop-by-hop routing due to the extra address vector overhead. However, for symmetric links, when the P2P mode DIO message is being multicast from the source hop-by- hop, receiving nodes can infer a next hop towards the source. When TargNode subsequently replies to the source along the established forward route, receiving nodes determine the next hop towards TargNode. In other words, it is efficient to use only routing tables for P2P-RDO message instead of "Address vector" for hop-by-hop routes (H=1) over symmetric links. RPL and P2P-RPL both specify the use of a single DODAG in networks of symmetric links, where the two directions of a link MUST both satisfy the constraints of the objective function. This eliminates the possibility to use asymmetric links which are qualified in one direction. But, application-specific routing requirements as defined in IETF ROLL Working Group [RFC5548], [RFC5673], [RFC5826] and [RFC5867] may be satisfied by routing paths using bidirectional asymmetric links. For this purpose, [I-D.thubert-roll-asymlink] describes bidirectional asymmetric links for RPL [RFC6550] with Paired DODAGs, for which the DAG root (DODAGID) is common for two Instances. This can satisfy application-specific routing requirements for bidirectional asymmetric links in core RPL [RFC6550]. Using P2P-RPL twice with Paired DODAGs, on the other hand, requires two roots: one for the source and another for the target node due to temporary DODAG formation. For networks composed of bidirectional asymmetric links (see Section 5), AODV-RPL specifies P2P route discovery, utilizing RPL with a new MoP. AODV-RPL makes Anamalamudi, et al. Expires September 6, 2018 [Page 3] Internet-Draft AODV-RPL March 2018 use of two multicast messages to discover possibly asymmetric routes, which can achieve higher route diversity. AODV-RPL eliminates the need for address vector control overhead in hop-by-hop mode. This significantly reduces the control packet size, which is important for Constrained LLN networks. Both discovered routes (upward and downward) meet the application specific metrics and constraints that are defined in the Objective Function for each Instance [RFC6552]. The route discovery process in AODV-RPL is modeled on the analogous procedure specified in AODV [RFC3561]. The on-demand nature of AODV route discovery is natural for the needs of peer-to-peer routing in RPL-based LLNs. AODV terminology has been adapted for use with AODV- RPL messages, namely RREQ for Route Request, and RREP for Route Reply. AODV-RPL currently omits some features compared to AODV -- in particular, flagging Route Errors, blacklisting unidirectional links, multihoming, and handling unnumbered interfaces. 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Additionally, this document uses the following terms: AODV Ad Hoc On-demand Distance Vector Routing[RFC3561]. AODV-RPL Instance Either the RREQ-Instance or RREP-Instance Asymmetric Route The route from the OrigNode to the TargNode can traverse different nodes than the route from the TargNode to the OrigNode. An asymmetric route may result from the asymmetry of links, such that only one direction of the series of links fulfills the constraints in route discovery. If the OrigNode doesn't require an upward route towards itself, the route is also considered as asymmetric. Bi-directional Asymmetric Link A link that can be used in both directions but with different link characteristics. DODAG RREQ-Instance (or simply RREQ-Instance) RPL Instance built using the DIO with RREQ option; used for control message transmission from OrigNode to TargNode, thus enabling data transmission from TargNode to OrigNode. DODAG RREP-Instance (or simply RREP-Instance) Anamalamudi, et al. Expires September 6, 2018 [Page 4] Internet-Draft AODV-RPL March 2018 RPL Instance built using the DIO with RREP option; used for control message transmission from TargNode to OrigNode thus enabling data transmission from OrigNode to TargNode. Downward Direction The direction from the OrigNode to the TargNode. Downward Route A route in the downward direction. hop-by-hop routing Routing when each node stores routing information about the next hop. OrigNode The IPv6 router (Originating Node) initiating the AODV-RPL route discovery to obtain a route to TargNode. Paired DODAGs Two DODAGs for a single route discovery process of an application. P2P Point-to-Point -- in other words, not constrained to traverse a common ancestor. RREQ-DIO message An AODV-RPL MoP DIO message containing the RREQ option. The RPLInstanceID in RREQ-DIO is assigned locally by the OrigNode. RREP-DIO message An AODV-RPL MoP DIO message containing the RREP option. The RPLInstanceID in RREP-DIO is typically paired to the one in the associated RREQ-DIO message. Source routing The mechanism by which the source supplies the complete route towards the target node along with each data packet [RFC6550]. Symmetric route The upstream and downstream routes traverse the same routers. Both directions fulfill the constraints in route discovery. TargNode The IPv6 router (Target Node) for which OrigNode requires a route and initiates Route Discovery within the LLN network. Upward Direction The direction from the TargNode to the OrigNode. Anamalamudi, et al. Expires September 6, 2018 [Page 5] Internet-Draft AODV-RPL March 2018 Upward Route A route in the upward direction. 3. Overview of AODV-RPL With AODV-RPL, routes from OrigNode to TargNode within the LLN network established are "on-demand". In other words, the route discovery mechanism in AODV-RPL is invoked reactively when OrigNode has data for delivery to the TargNode but existing routes do not satisfy the application's requirements. The routes discovered by AODV-RPL are point-to-point; in other words the routes are not constrained to traverse a common ancestor. Unlike core RPL [RFC6550] and P2P-RPL [RFC6997], AODV-RPL can enable asymmetric communication paths in networks with bidirectional asymmetric links. For this purpose, AODV-RPL enables discovery of two routes: namely, one from OrigNode to TargNode, and another from TargNode to OrigNode. When possible, AODV-RPL also enables symmetric route discovery along Paired DODAGs (see Section 5). In AODV-RPL, route discovery is initiated by forming a temporary DAG rooted at the OrigNode. Paired DODAGs (Instances) are constructed according to a new AODV-RPL Mode of Operation (MoP) during route formation between the OrigNode and TargNode. The RREQ-Instance is formed by route control messages from OrigNode to TargNode whereas the RREP-Instance is formed by route control messages from TargNode to OrigNode (as shown in Figure 4). Intermediate routers join the Paired DODAGs based on the rank as calculated from the DIO message. Henceforth in this document, the RREQ-DIO message means the AODV-RPL mode DIO message from OrigNode to TargNode, containing the RREQ option. Similarly, the RREP-DIO message means the AODV-RPL mode DIO message from TargNode to OrigNode, containing the RREP option. Subsequently, the route discovered in the RREQ-Instance is used for data transmission from TargNode to OrigNode, and the route discovered in RREP-Instance is used for Data transmission from OrigNode to TargNode. 4. AODV-RPL DIO Options 4.1. AODV-RPL DIO RREQ Option A RREQ-DIO message MUST carry exactly one RREQ option. Anamalamudi, et al. Expires September 6, 2018 [Page 6] Internet-Draft AODV-RPL March 2018 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Option Length |S|H|X| Compr | L | MaxRank | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Orig SeqNo | | +-+-+-+-+-+-+-+-+ | | | | | | Address Vector (Optional, Variable Length) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: DIO RREQ option format for AODV-RPL MoP OrigNode supplies the following information in the RREQ option of the RREQ-Instance message: Type The type of the RREQ option(see Section 9.2). Option Length Length of the option in octets excluding the Type and Length fields. Variable due to the presence of the address vector and the number of octets elided according to the Compr value. S Symmetric bit indicating a symmetric route from the OrigNode to the router issuing this RREQ-DIO. The bit SHOULD be set to 1 in the RREQ-DIO when the OrigNode initiates the route discovery. X Reserved. H The OrigNode sets this flag to one if it desires a hop-by-hop route. It sets this flag to zero if it desires a source route. This flag is valid to both downstream route and upstream route. Compr Anamalamudi, et al. Expires September 6, 2018 [Page 7] Internet-Draft AODV-RPL March 2018 4-bit unsigned integer. Number of prefix octets that are elided from the Address Vector. The octets elided are shared with the IPv6 address in the DODAGID. L 2-bit unsigned integer. This field indicates the duration that a node joining the temporary DAG in RREQ-Instance, including the OrigNode and the TargNode. Once the time is reached, a node MUST leave the DAG and stop sending or receiving any more DIOs for the temporary DODAG. The detailed definition can be found in [RFC6997]. * 0x00: No duration time imposed. * 0x01: 2 seconds * 0x02: 16 seconds * 0x03: 64 seconds It should be indicated here that L is not the route lifetime, which is defined in the DODAG configuration option. The route entries in hop-by-hop routing and states of source routing can still be maintained even after the DAG expires. MaxRank This field indicates the upper limit on the integer portion of the rank. A node MUST NOT join a temporary DODAG if its own rank would equal to or higher than the limit. A value of 0 in this field indicates the limit is infinity. For more details please refer to [RFC6997]. OrigNode Sequence Number Sequence Number of OrigNode, defined similarly as in AODV [RFC3561]. Address Vector (Optional) A vector of IPv6 addresses representing the route that the RREQ- DIO has passed. It is only present when the 'H' bit is set to 0. The prefix of each address is elided according to the Compr field. 4.2. AODV-RPL DIO RREP Option A RREP-DIO message MUST carry exactly one RREP option. The TargNode supplies the following information in the RREP option: Anamalamudi, et al. Expires September 6, 2018 [Page 8] Internet-Draft AODV-RPL March 2018 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Option Length |H|X| Compr | L | MaxRank | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |T|G| SHIFT | Reserved | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | | Address Vector (Optional, Variable Length) | . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: DIO RREP option format for AODV-RPL MoP Type The type of the RREP option (see Section 9.2) Option Length Length of the option in octets excluding the Type and Length fields. Variable due to the presence of the address vector and the number of octets elided according to the Compr value. H This bit indicates the downstream route is source routing (H=0) or hop-by-hop (H=1). It SHOULD be set to be the same as the 'H' bit in RREQ option. X Reserved. Compr 4-bit unsigned integer. Same definition as in RREQ option. L 2-bit unsigned integer with the same definition as in Section 4.1. MaxRank Same definition as in RREQ option. T 'T' is set to 1 to indicate that the RREP-DIO MUST include exactly one AODV-RPL Target Option. Otherwise, the Target Option is not necessary in the RREP-DIO. G Anamalamudi, et al. Expires September 6, 2018 [Page 9] Internet-Draft AODV-RPL March 2018 Gratuitous route (see Section 7). SHIFT 6-bit unsigned integer. This field indicates the how many the original InstanceID (see Section 6.3.3) is shifted (added an integer from 0 to 63). 0 indicates that the original InstanceID is used. Reserved Reserved for future usage; MUST be initialized to zero and MUST be ignored upon reception. Address Vector (Optional) It is only present when the 'H' bit is set to 0. For an asymmetric route, it is a vector of IPv6 addresses representing the route that the RREP-DIO has passed. For symmetric route, it is the accumulated vector when the RREQ-DIO arrives at the TargNode. 4.3. AODV-RPL DIO Target Option The AODV-RPL Target Option is defined based on the Target Option in core RPL [RFC6550]: the Destination Sequence Number of the TargNode is added. A RREQ-DIO message MUST carry at least one AODV-RPL Target Options. A RREP-DIO message MUST carry exactly one AODV-RPL Target Option encapsulating the address of the OrigNode if the 'T' bit is set to 1. If an OrigNode want to discover routes to multiple TargNodes, and these routes share the same constraints, then the OrigNode can include all the addresses of the TargNodes into multiple AODV-RPL Target Options in the RREQ-DIO, so that the cost can be reduced to building only one DODAG. Different addresses of the TargNodes can merge if they share the same prefix. Anamalamudi, et al. Expires September 6, 2018 [Page 10] Internet-Draft AODV-RPL March 2018 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Option Length | Dest SeqNo | Prefix Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + | | Target Prefix (Variable Length) | . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: Target option format for AODV-RPL MoP Type The type of the AODV-RPL Target Option (see Section 9.2) Destination Sequence Number In RREQ-DIO, if nonzero, it is the last known Sequence Number for TargNode for which a route is desired. In RREP-DIO, it is the destination sequence number associated to the route. 5. Symmetric and Asymmetric Routes In Figure 4 and Figure 5, BR is the BorderRouter, O is the OrigNode, R is an intermediate router, and T is the TargNode. If the RREQ-DIO arrives over an interface that is known to be symmetric, and the 'S' bit is set to 1, then it remains as 1, as illustrated in Figure 4. An intermediate router sends out RREQ-DIO with the 'S' bit set to 1, meaning that all the one-hop links on the route from the OrigNode to this router meet the requirements of route discovery; thus the route can be used symmetrically. Anamalamudi, et al. Expires September 6, 2018 [Page 11] Internet-Draft AODV-RPL March 2018 BR / | \ / | \ / | \ R R R / \ | / \ / \ | / \ / \ | / \ R -------- R --- R ----- R -------- R / \ <--S=1--> / \ <--S=1--> / \ <--S=1--> \ / \ / <--S=1--> / \ / \ / \ O ---------- R ------ R------ R ----- R ----------- T / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ R ----- R ----------- R ----- R ----- R ----- R ---- R----- R >---- RREQ-Instance (Control: S-->D; Data: D-->S) -------> <---- RREP-Instance (Control: D-->S; Data: S-->D) -------< Figure 4: AODV-RPL with Symmetric Paired Instances Upon receiving a RREQ-DIO with the 'S' bit set to 1, a node MUST decide if this one-hop link can be used symmetrically, i.e., both the two directions meet the requirements of data transmission. If the RREQ-DIO arrives over an interface that is not known to be symmetric, or is known to be asymmetric, the 'S' bit is set to 0. Moreover, if the 'S' bit arrives already set to be '0', it is set to be '0' on retransmission (Figure 5). Therefore, for asymmetric route, there is at least one hop which doesn't fulfill the constraints in the two directions. Based on the 'S' bit received in RREQ-DIO, the TargNode decides whether or not the route is symmetric before transmitting the RREP-DIO message upstream towards the OrigNode. The criterion and the corresponding metric used to determine if a one-hop link is symmetric or not is implementation specific and beyond the scope of the document. Also, the difference in the metric values for upward and downward directions of a link that can be establish its symmetric and asymmetric nature is implementation specific. For instance, the intermediate routers MAY choose to use local information (e.g., bit rate, bandwidth, number of cells used in 6tisch), a priori knowledge (e.g. link quality according to previous communication) or estimate the metric using averaging techniques or any other means that is appropriate to the application context. Anamalamudi, et al. Expires September 6, 2018 [Page 12] Internet-Draft AODV-RPL March 2018 Appendix A describes an example method using the ETX and RSSI to estimate whether the link is symmetric in terms of link quality is given in using an averaging technique. BR / | \ / | \ / | \ R R R / \ | / \ / \ | / \ / \ | / \ R --------- R --- R ---- R --------- R / \ --S=1--> / \ --S=0--> / \ --S=1--> \ / \ / --S=0--> / \ / \ / \ O ---------- R ------ R------ R ----- R ----------- T / \ / \ / \ / \ / <--S=0-- / \ / \ / <--S=0-- / \ / \ / \ / \ R ----- R ----------- R ----- R ----- R ----- R ---- R----- R <--S=0-- <--S=0-- <--S=0-- <--S=0-- <--S=0-- >---- RREQ-Instance (Control: S-->D; Data: D-->S) -------> <---- RREP-Instance (Control: D-->S; Data: S-->D) -------< Figure 5: AODV-RPL with Asymmetric Paired Instances 6. AODV-RPL Operation 6.1. Generating Route Request at OrigNode The route discovery process is initiated on-demand when an application at the OrigNode has data to be transmitted to the TargNode, but no route for the target exists or the current routes don't fulfill the requirements of the data transmission. In this case, the OrigNode MUST build a local RPLInstance and a DODAG rooted at itself. Then it begins to send out DIO message in AODV-RPL MoP via link-local multicast. The DIO MUST contain exactly one RREQ option as defined in Section 4.1, and at least one AODV-RPL Target Option as defined in Figure 3. This DIO message is noted as RREQ- DIO. The 'S' bit in RREQ-DIO sent out by the OrigNode is set as 1. The maintenance of Originator and Destination Sequence Number in the RREQ option is as defined in AODV [RFC3561]. The address in the AODV-RPL Target Option can be a unicast IPv6 address, a prefix or a multicast address. The OrigNode can initiate Anamalamudi, et al. Expires September 6, 2018 [Page 13] Internet-Draft AODV-RPL March 2018 the route discovery process for multiple targets simultaneously by including multiple AODV-RPL Target Options, and within a RREQ-DIO the requirements for the routes to different TargNodes MUST be the same. The OrigNode can maintain different RPLInstances to discover routes with different requirements to the same targets. Due to the InstanceID pairing mechanism Section 6.3.3, route replies (RREP-DIOs) from different paired RPLInstances can be distinguished. The transmission of RREQ-DIO follows the Trickle timer. When the L duration has transpired, the OrigNode MUST leave the DODAG and stop sending any RREQ-DIOs in the related RPLInstance. 6.2. Receiving and Forwarding Route Request Upon receiving a RREQ-DIO, a router out of the RREQ-instance goes through the following steps: Step 1: If the 'S' bit in the received RREQ-DIO is set to 1, the router MUST look into the two directions of the link by which the RREQ- DIO is received. In case that the downward (i.e. towards the TargNode) direction of the link can't fulfill the requirements, then the link can't be used symmetrically, thus the 'S' bit of the RREQ-DIO to be send out MUST be set as 0. If the 'S' bit in the received RREQ-DIO is set to 0, the router MUST look only into the upward direction (i.e. towards the OrigNode) of the link. If the upward direction of the link can fulfill the requirements indicated in the constraint option, and the router's rank would be inferior to the MaxRank limit, the router chooses to join in the DODAG of the RREQ-Instance. The router issuing the received RREQ- DIO is selected as the preferred parent. Afterwards, other RREQ- DIO message can be received. How to maintain the parent set, select the preferred parent, and update the router's rank follows the core RPL and the OFs defined in ROLL WG. In case that the constraint or the MaxRank limit is not fulfilled, the router MUST NOT join in the DODAG. Otherwise, go to the following steps 2, 3, 4 and 5. A router MUST discard a received RREQ-DIO if the advertised rank equals or exceeds the MaxRank limit. Step 2: Then the router checks if one of its addresses is included in one of the AODV-RPL Target Options or belongs to the indicated Anamalamudi, et al. Expires September 6, 2018 [Page 14] Internet-Draft AODV-RPL March 2018 multicast group. If so, this router is one of the TargNodes. Otherwise, it is an intermediate router. Step 3: If the 'H' bit is set to 1, then the router (TargNode or intermediate) MUST build route entry towards its preferred parent. The route entry SHOULD be stored along with the associated RPLInstanceID and DODAGID. If the 'H' bit is set to 0, an intermediate router MUST include the address of the interface receiving the RREQ-DIO into the address vector. Step 4: If there are multiple AODV-RPL Target Options in the received RREQ-DIO, a TargNode SHOULD continue sending RREQ-DIO to reach other targets. When preparing its own RREQ-DIO, the TargNode MUST delete the AODV-RPL Target Option related to its own address, so that the routers which higher ranks would know the route to this target has already been found. When an intermediate router receives several RREQ-DIOs which include different lists of AODV- RPL Target Options, the intersection of these lists will be included in its own RREQ-DIO. If the intersection is empty, the router SHOULD NOT send out any RREQ-DIO. Any RREQ-DIO message with different AODV-RPL Target Options coming from a router with higher rank is ignored. Step 5: For an intermediate router, it sends out its own RREQ-DIO via link-local multicast. For a TargNode, it can begin to prepare the RREP-DIO. 6.3. Generating Route Reply at TargNode 6.3.1. RREP-DIO for Symmetric route When a RREQ-DIO arrives at a TargNode with the 'S' bit set to 1, it means there exists a symmetric route in which the two directions can fulfill the requirements. Other RREQ-DIOs can bring the upward direction of asymmetric routes (i.e. S=0). How to choose between a qualified symmetric route and an asymmetric route hopefully having better performance is implementation-specific and out of scope. If the implementation choose to use the symmetric route, the TargNode MAY send out the RREP-DIO after a duration RREP_WAIT_TIME to wait for the convergence of RD to an optimal symmetric route. Anamalamudi, et al. Expires September 6, 2018 [Page 15] Internet-Draft AODV-RPL March 2018 For symmetric route, the RREP-DIO message is sent via unicast to the OrigNode; therefore the DODAG in RREP-Instance doesn't need to be actually built. The RPLInstanceID in the RREP-Instance is paired as defined in Section 6.3.3. The 'S' bit in the base DIO remains as 1. In the RREP option, The 'SHIFT' field and the 'T' bit are set as defined in Section 6.3.3. The address vector received in the RREQ- DIO MUST be included in this RREP option in case the 'H' bit is set to 0 (both in RREQ-DIO and RREP-DIO). If the 'T' bit is set to 1, the address of the OrigNode MUST be encapsulated in an AODV-RPL Target Option and included in this RREP-DIO message, and the Destination Sequence Number is set according to AODV [RFC3561]. 6.3.2. RREP-DIO for Asymmetric Route When a RREQ-DIO arrives at a TargNode with the 'S' bit set to 0, the TargNode MUST build a DODAG in the RREP-Instance rooted at itself in order to discover the downstream route from the OrigNode to the TargNode. The RREP-DIO message MUST be send out via link-local multicast until the OrigNode is reached or the MaxRank limit is exceeded. The settings of the RREP-DIO are the same as in symmetric route. 6.3.3. RPLInstanceID Pairing Since the RPLInstanceID is assigned locally (i.e., there is no coordination between routers in the assignment of RPLInstanceID) the tuple (RPLInstanceID, DODAGID, Address in the AODV-RPL Target Option) is needed to uniquely identify a DODAG in an AODV-RPL instance. Between the OrigNode and the TargNode, there can be multiple AODV-RPL instances when applications upper layer have different requirements. Therefore the RREQ-Instance and the RREP-Instance in the same route discovery MUST be paired. The way to realize this is to pair their RPLInstance IDs. Typically, the two InstanceIDs are set as the local InstanceID in core RPL: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |1|D| ID | Local RPLInstanceID in 0..63 +-+-+-+-+-+-+-+-+ Figure 6: Local Instance ID The first bit is set to 1 indicating the RPLInstanceID is local. The 'D' bit here is used to distinguish the two AODV-RPL instances: D=0 for RREQ-Instance, D=1 for RREP-Instance. The ID of 6 bits SHOULD be Anamalamudi, et al. Expires September 6, 2018 [Page 16] Internet-Draft AODV-RPL March 2018 the same for RREQ-Instance and RREP-Instance. Here, the 'D' bit is used slightly differently than in RPL. When preparing the RREP-DIO, a TargNode could find the RPLInstanceID to be used for the RREP-Instance is already occupied by another instance from an earlier route discovery operation which is still active. In other words, two OrigNodes need routes to the same TargNode and they happen to use the same RPLInstanceID for RREQ- Instance. In this case, the occupied RPLInstanceID MUST NOT be used again. Then this RPLInstanceID SHOULD be shifted into another integer and shifted back to the original one at the OrigNode. In RREP option, the SHIFT field indicates the how many the original RPLInstanceID is shifted. When the new InstanceID after shifting exceeds 63, it will come back counting from 0. For example, the original InstanceID is 60, and shifted by 6, the new InstanceID will be 2. The 'T' MUST be set to 1 to make sure the two RREP-DIOs can be distinguished by the address of the OrigNode in the AODV-RPL Target Option. 6.4. Receiving and Forwarding Route Reply Upon receiving a RREP-DIO, a router out of the RREP-Instance goes through the following steps: Step 1: If the 'S' bit of the RREP-DIO is set to 0, the router MUST look into the downward direction of the link (towards the TargNode) by which the RREP-DIO is received. If the downward direction of the link can fulfill the requirements indicated in the constraint option, and the router's rank would be inferior to the MaxRank limit, the router chooses to join in the DODAG of the RREP- Instance. The router issuing the received RREP-DIO is selected as the preferred parent. Afterwards, other RREQ-DIO messages can be received. How to maintain the parent set, select the preferred parent, and update the router's rank follows the core RPL and the OFs defined in ROLL WG. If the constraints are not fulfilled, the router MUST NOT join in the DODAG, and will not go through steps 2, 3, and 4. A router MUST discard a received RREQ-DIO if the advertised rank equals or exceeds the MaxRank limit. If the 'S' bit is set to 1, the router does nothing in this step. Step 2: Anamalamudi, et al. Expires September 6, 2018 [Page 17] Internet-Draft AODV-RPL March 2018 Then the router checks if one of its addresses is included in the AODV-RPL Target Option. If so, this router is the OrigNode of the route discovery. Otherwise, it is an intermediate router. Step 3: If the 'H' bit is set to 1, then the router (OrigNode or intermediate) MUST build route entry including the RPLInstanceID of RREP-Instance and the DODAGID. For symmetric route, the route entry is to the router from which the RREP-DIO is received. For asymmetric route, the route entry is to the preferred parent in the DODAG of RREQ-Instance. If the 'H' bit is set to 0, for asymmetric route, an intermediate router MUST include the address of the interface receiving the RREP-DIO into the address vector, and for symmetric route, there is nothing to do in this step. Step 4: For an intermediate router, in case of asymmetric route, the RREP- DIO is sent out via link-local multicast; in case of symmetric route, the RREP-DIO is unicasted to the OrigNode via the next hop in source routing (H=0), or via the next hop in the route entry built in the RREQ-Instance (H=1). For the OrigNode, it can start transmitting the application data to TargNode along the path as discovered through RREP-Instance. 7. Gratuitous RREP In some cases, an Intermediate router that receives a RREQ-DIO message MAY transmit a "Gratuitous" RREP-DIO message back to OrigNode instead of continuing to multicast the RREQ-DIO towards TargNode. The intermediate router effectively builds the RREP-Instance on behalf of the actual TargNode. The 'G' bit of the RREP option is provided to distinguish the Gratuitous RREP-DIO (G=1) sent by the Intermediate node from the RREP-DIO sent by TargNode (G=0). The gratuitous RREP-DIO can be sent out when an intermediate router R receives a RREQ-DIO for a TargNode T, and R happens to have both forward and reverse routes to T which also fulfill the requirements. In case of source routing, the intermediate router R MUST unicast the received RREQ-DIO to TargNode T including the address vector between the OrigNode O and the router R. Thus T can have a complete address vector between O and itself. Then T MUST unicast a RREP-DIO including the address vector between T and R. Anamalamudi, et al. Expires September 6, 2018 [Page 18] Internet-Draft AODV-RPL March 2018 In case of hop-by-hop routing, R MUST unicast the received RREQ-DIO to T. The routers along the route SHOULD build new route entries with the related RPLInstanceID and DODAGID in the downward direction. Then T MUST unicast the RREP-DIO to R, and the routers along the route SHOULD build new route entries in the upward direction. Upon received the unicast RREP-DIO, R sends the gratuitous RREP-DIO to the OrigNode as the same way defined in Section 6.3. 8. Operation of Trickle Timer The trickle timer operation to control RREQ-Instance/RREP-Instance multicast is similar to that in P2P-RPL [RFC6997]. 9. IANA Considerations 9.1. New Mode of Operation: AODV-RPL IANA is required to assign a new Mode of Operation, named "AODV-RPL" for Point-to-Point(P2P) hop-by-hop routing under the RPL registry. The value of TBD1 is assigned from the "Mode of Operation" space [RFC6550]. +-------------+---------------+---------------+ | Value | Description | Reference | +-------------+---------------+---------------+ | TBD1 (5) | AODV-RPL | This document | +-------------+---------------+---------------+ Figure 7: Mode of Operation 9.2. AODV-RPL Options: RREQ, RREP, and Target Three entries are required for new AODV-RPL options "RREQ", "RREP" and "AODV-RPL Target" with values of TBD2 (0x0A), TBD3 (0x0B) and TBD4 (0x0C) from the "RPL Control Message Options" space [RFC6550]. +-------------+------------------------+---------------+ | Value | Meaning | Reference | +-------------+------------------------+---------------+ | TBD2 (0x0A) | RREQ Option | This document | +-------------+------------------------+---------------+ | TBD3 (0x0B) | RREP Option | This document | +-------------+------------------------+---------------+ | TBD3 (0x0C) | AODV-RPL Target Option | This document | +-------------+------------------------+---------------+ Figure 8: AODV-RPL Options Anamalamudi, et al. Expires September 6, 2018 [Page 19] Internet-Draft AODV-RPL March 2018 10. Security Considerations This document does not introduce additional security issues compared to base RPL. For general RPL security considerations, see [RFC6550]. 11. Future Work There has been some discussion about how to determine the initial state of a link after an AODV-RPL-based network has begun operation. The current draft operates as if the links are symmetric until additional metric information is collected. The means for making link metric information is considered out of scope for AODV-RPL. In the future, RREQ and RREP messages could be equipped with new fields for use in verifying link metrics. In particular, it is possible to identify unidirectional links; an RREQ received across a unidirectional link has to be dropped, since the destination node cannot make use of the received DODAG to route packets back to the source node that originated the route discovery operation. This is roughly the same as considering a unidirectional link to present an infinite cost metric that automatically disqualifies it for use in the reverse direction. 12. References 12.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On- Demand Distance Vector (AODV) Routing", RFC 3561, DOI 10.17487/RFC3561, July 2003, . [RFC5548] Dohler, M., Ed., Watteyne, T., Ed., Winter, T., Ed., and D. Barthel, Ed., "Routing Requirements for Urban Low-Power and Lossy Networks", RFC 5548, DOI 10.17487/RFC5548, May 2009, . [RFC5673] Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T. Phinney, "Industrial Routing Requirements in Low-Power and Lossy Networks", RFC 5673, DOI 10.17487/RFC5673, October 2009, . Anamalamudi, et al. Expires September 6, 2018 [Page 20] Internet-Draft AODV-RPL March 2018 [RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation Routing Requirements in Low-Power and Lossy Networks", RFC 5826, DOI 10.17487/RFC5826, April 2010, . [RFC5867] Martocci, J., Ed., De Mil, P., Riou, N., and W. Vermeylen, "Building Automation Routing Requirements in Low-Power and Lossy Networks", RFC 5867, DOI 10.17487/RFC5867, June 2010, . [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, JP., and R. Alexander, "RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks", RFC 6550, DOI 10.17487/RFC6550, March 2012, . [RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing Protocol for Low-Power and Lossy Networks (RPL)", RFC 6552, DOI 10.17487/RFC6552, March 2012, . [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and J. Martocci, "Reactive Discovery of Point-to-Point Routes in Low-Power and Lossy Networks", RFC 6997, DOI 10.17487/RFC6997, August 2013, . [RFC6998] Goyal, M., Ed., Baccelli, E., Brandt, A., and J. Martocci, "A Mechanism to Measure the Routing Metrics along a Point- to-Point Route in a Low-Power and Lossy Network", RFC 6998, DOI 10.17487/RFC6998, August 2013, . 12.2. Informative References [I-D.thubert-roll-asymlink] Thubert, P., "RPL adaptation for asymmetrical links", draft-thubert-roll-asymlink-02 (work in progress), December 2011. Appendix A. ETX/RSSI Values to select S bit We have tested the combination of "RSSI(downstream)" and "ETX (upstream)" to decide whether the link is symmetric or asymmetric at the intermediate nodes. The example of how the ETX and RSSI values are used in conjuction is explained below: Anamalamudi, et al. Expires September 6, 2018 [Page 21] Internet-Draft AODV-RPL March 2018 Source---------->NodeA---------->NodeB------->Destination Figure 9: Communication link from Source to Destination +-------------------------+----------------------------------------+ | RSSI at NodeA for NodeB | Expected ETX at NodeA for NodeB->NodeA | +-------------------------+----------------------------------------+ | > -15 | 150 | | -25 to -15 | 192 | | -35 to -25 | 226 | | -45 to -35 | 662 | | -55 to -45 | 993 | +-------------------------+----------------------------------------+ Table 1: Selection of 'S' bit based on Expected ETX value We tested the operations in this specification by making the following experiment, using the above parameters. In our experiment, a communication link is considered as symmetric if the ETX value of NodeA->NodeB and NodeB->NodeA (See Figure.8) are, say, within 1:3 ratio. This ratio should be taken as a notional metric for deciding link symmetric/asymmetric nature, and precise definition of the ratio is beyond the scope of the draft. In general, NodeA can only know the ETX value in the direction of NodeA -> NodeB but it has no direct way of knowing the value of ETX from NodeB->NodeA. Using physical testbed experiments and realistic wireless channel propagation models, one can determine a relationship between RSSI and ETX representable as an expression or a mapping table. Such a relationship in turn can be used to estimate ETX value at nodeA for link NodeB--->NodeA from the received RSSI from NodeB. Whenever nodeA determines that the link towards the nodeB is bi-directional asymmetric then the "S" bit is set to "S=0". Later on, the link from NodeA to Destination is asymmetric with "S" bit remains to "0". Appendix B. Changes to version 02 o Include the support for source routing. o Bring some features from [RFC6997], e.g., choice between hop-by- hop and source routing, duration of residence in the DAG, MaxRank, etc. o Define new target option for AODV-RPL, including the Destination Sequence Number in it. Move the TargNode address in RREQ option and the OrigNode address in RREP option into ADOV-RPL Target Option. o Support route discovery for multiple targets in one RREQ-DIO. Anamalamudi, et al. Expires September 6, 2018 [Page 22] Internet-Draft AODV-RPL March 2018 o New InstanceID pairing mechanism. Authors' Addresses Satish Anamalamudi Huaiyin Institute of Technology No.89 North Beijing Road, Qinghe District Huaian 223001 China Email: satishnaidu80@gmail.com Mingui Zhang Huawei Technologies No. 156 Beiqing Rd. Haidian District Beijing 100095 China Email: zhangmingui@huawei.com Abdur Rashid Sangi Huaiyin Institute of Technology No.89 North Beijing Road, Qinghe District Huaian 223001 P.R. China Email: sangi_bahrian@yahoo.com Charles E. Perkins Futurewei 2330 Central Expressway Santa Clara 95050 Unites States Email: charliep@computer.org S.V.R Anand Indian Institute of Science Bangalore 560012 India Email: anand@ece.iisc.ernet.in Anamalamudi, et al. Expires September 6, 2018 [Page 23] Internet-Draft AODV-RPL March 2018 Bing Liu Huawei Technologies No. 156 Beiqing Rd. Haidian District Beijing 100095 China Email: remy.liubing@huawei.com Anamalamudi, et al. Expires September 6, 2018 [Page 24]